Embryos containing DNA from three parents have been created from human eggs
for the first time in a breakthrough for a therapy which could eradicate a
host of rare genetic disorders.

Eggs containing DNA from two women were fertilised and grown into healthy embryos in a lab experiment by researchers from Oregon Health & Science University in the US.

The technique is designed for women who have mutations in tiny structures known as mitochondria, which can result in a range of devastating conditions including muscular dystrophy.

It involves taking chromosomes from the mother's egg, which carry 99.8 per cent of her DNA, and placing them in a donor egg which has healthy mitochondria but has had its own chromosomes removed.

The eggs were fertilised by sperm and almost half developed into healthy embryos. The resulting children would have inherited 99.8 per cent of their DNA from their parents, but also a tiny fraction from the donor.

Writing in the Nature journal, the researchers reported that half of the embryos developed abnormally, but identified improvements in their technique which could improve its success rate.

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A separate team from Newcastle University has already successfully demonstrated a similar technique, where the mother's DNA is transferred after the egg is fertilised and not before.

Their method, which is still being fine-tuned, has a much lower risk of defective embryos but may raise fewer ethical concerns because the DNA transfer happens before the egg has been fertilised, experts said.

The Human Fertilisation and Embryology Authority is currently consulting on a change in the law which would allow the creation of IVF babies using either technique.

The Oregon researchers reported that tests of their technique on rhesus monkeys had shown it could create healthy offspring, but added that there were fewer issues with the quality of embryos than in humans.

Prof Robin Lovell-Badge, of the MRC National Institute for Medical Research, said: "In the current study, about half the manipulated eggs failed to fertilise properly, and consequently these gave abnormal embryos.

"While these are clearly recognisable, and could be discarded, this substantially lowers the efficiency of the procedure ... it is therefore conceivable that the other proposed method, where the nuclear genetic material is transferred after fertilisation, will be more robust."